Power transmission



June 3, 1941.

F. T. HARRINGTON ETAL POWER TRANSMISSION Filed July 13, 1939 lac 70 J FIG. I ea K14 I 54 ea Me ea 1 0 I so :0 4 a4 INVENTORS FERRIS T. HARRINGTON CLIFFORD V. LOSEY 8- RAYMOND S. MILLER ATTORNEY Patented June 3, 1941 I POWER TRANSMISSION Ferris '1. Harrington, Cliflord V. Loser, and Baymond S. Miller, Detroit,

Mich, assignors to Vicken Incorporated, Detroit, Mich, a corporation of Application July 13,1939, Serial No. 284,208

I '1 Claims. The present invention relates to power trans- -mission of the hydraulic type and particularly to a pressure switch for use in power transmis sions of this character. Such a power transmission generally comprises a source of pressure, such as a pump, together with one or more fluid motors which are driven by pressure fluid supplied from the pump. Control means such as directional valves are usually provided for selectively controlling the flow of fluid to the motor, and such control means are frequently operated electrically as by solenoids.

It is frequently desirable to shift such control means in dependence upon the rise in pressure at a certain point in the system, and for this purpose pressure switches have heretofore been employed. One of the most common control systems of this type utilizes a pressure switch hydraulically connected with the pressure side of a hydraulic motor so that the switch is operated when a predetermined pressure is applied to the motor. Since the pressure applied to the motor depends entirely upon the resistance which the motor encounters in doing its work and since this resistance is subject frequently to momentary fluctuations of varying magnitude, considerable difficulty is frequently encountered with pressure switches of the prior art due to their responding to these momentary fluctuations at a time when no response is desired, thus producing faulty operation of the system.

The number of different possible hydraulic circuits in which a pressure switch may be used is almost countless, each circuit requiring slightly different characteristics in the pressure switch for satisfactory operation. It isdesirable in the manufacture of a line of pressure switches for use in this field to have as few different models as possible and yet to be able to provide a pressure switch having suitable characteristics for any particular circuit application which may be proposed.

It is an object of the present invention accordingly to provide an improved pressure responsive switch which is adapted for installation in circuits having widely difl'erent characteristics and which may be made to respond to pressure rises of any desired degree and of any desired speed.

A fury'ther object is to provide a pressure switch of this character of simple and reliable construction which is inexpensive to manufacture and which is readily adaptable to various conditions by a simple substitution of inexpensive parts modifled form of readily accessible from the outside of the switch mechanism.

Further objects and advantages of the present invention will be apparent from the followin description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearlyshown.

In the drawing:

Figure 1 is a longitudinal cross section of a pressure switch embody s a preferred form of the present invention.

Figure 2 is a cross section on line 2-2 of Figure 1.

Figure 3 is afragmentary cross section corresponding to a portion of Figure 1 showing a the end cap illustrated in Figure 1.

A main body member I0 is provided with a longitudinal bore i2 having an enlarged chamber l4 at the upper end thereof and an oil seal l6 at the-lower end thereof. Slidably mounted within the bore I2 is a piston l8. Theiatter has an annular groove 20 substantially at its mid portion and an annular groove 22 near the upper end thereof. A flange 24 provided with one or more fluid conducting notches 26 at the lower corner thereof is provided at the top end of the piston l8. The piston i8 is formed with one or more passages connecting the annular grooves 20 and 22. In the form illustrated this passage is formed as a flat 28 (Figure 2), only one such passage being illustrated, thereby providing a path of predetermined resistance between the chamber l4 and the annular groove 20.

The bore I2 is provided with a lateral outlet port 30 in which an interchangeable bushing 32 is mounted. The latter serves as a pipe connec-' tion to which a suitable conduit may be screwed for draining fluid to the usual oil sump. The bushing 32 is provided with a small oriflce 34 of predetermined resistance, it being understood that bushings having oriflces 34 of diflerent size may be readily substituted for that shown in the drawing.

Secured to the lower face of the body ill by a suitable fastening means, not shown, is a switch enclosure l 36 carrying a suitable snap-acting, double-throw switch generally designated as 38, the details of which per se form no part of the present invention. Slidably mounted in holes 40 in the casing 36 is a switch-operating plunger 42 which is biased to an upward position illustrated by a suitable spring 44. Mounted between the top of the housing 36 and the upper end of a bore 46 in the piston i8 is a spring 48 which normally biases the piston [8 to the upper posi-- tion illustrated, a suitable spring-guiding stud 88 being mounted at the upper end of spring 48 and providing a predetermined clearance at 52 with the upper end of plunger 42.

Secured to the upper end of the body I8 is a cap member 54 having a conduit connection 58' at the upper end thereof adapted to receive a bushing 58 similar to the bushing 32 except that it is provided with a larger orifice 88 than the orifice 34. Communicating with the connection 58 is a transverse passage 82 having a valve seat 84 therein adapted to receive a ball valve 88. The latter is urged to the seat by a spring 88 which is adjustable by means of a threaded abutment plunger 18. A vertical passage 12 connects between the chamber 14, in which theball and spring 88 are mounted, and the chamber l4 in body I. I f

In operation, the bushing 58 having been connected to the point in the hydraulic system at which a pressure rise occurs and to which rise the switch is to respond, it will be seen that a predetermined rise in pressure in the connection 58 and conduit 82 will lift the ball 88 from its seat. The pressure at which this occurs depends upon the setting of the spring '88 which may be readily adjusted by the plunger 18.

When the ball 88 lifts, pressure fluid is admitted to the chamber l4 through conduit 12. There is, however, a path of escape'from the chamber l4- through the passageway 28 to the annular groove 28 and through orifice' 34 anti connection 82 to the sump. This path is re stricted, however, by the passage 28 to a limited degree and by the orifice 34 to a larger degree.

Thus it will be seen that in order for the piston l8 to move downwardly against the force of the spring 48 it is necessary that such pressure exist in conduit 82 as will lift the ball 88 far enough to pass oil into chamber I4 at a greater rate than it can pass out through orifice 84. Wheneven this pressure is exceeded, the piston l8 will move down taking up the clearance at 82 and thereafter depressing plunger 42 to shift the switch 38.

As soon as the pressure in conduit 82 falls below the point where the piston i8 has started moving, the latter will start to move upwardly permitting spring 44 to lift the plunger 42 and restore the switch 38 to, itsoriginal position. During this action the ball valve 88 closes and the ofl displaced from chamber l4 escapes through the passage 28 and orifice 34 to the sump.

It will be seen that by substitution oi bushings 82 having orifices of smaller or greater size that the relationship between the speed of rise of pressure in conduit 82 and the speed of movement of piston 18 may be controlled as desired. It is preferred to utilize the single passageway 28 in the piston '8, thus acting as a minimum restriction between v, chamber I 4 and connection 32 which may be utilized for slowing down the piston movement to a maximum extent by providing a bushing 32 with an orifice of negli-.

gible resistance.

Still furthercontrol of the speed of movement of piston l8 may be obtained by substituting for the bushing 58 one having a smaller orifice 80, thus limiting the speed at which sudden pressure rises in the conduit beyond bushing 58 may be transmitted to the conduit 82. The smaller oriflce 88 must, however, be one which has less resistance than the combined resistance of the passage 28 and the particular orifice 84 being used.

Certain applications require that when the switch 38 is once operated by a pressure rise transmitted to the piston l8, the switch must remain in its shifted position until the pressure in conduit 82 has dropp d practically to zero. For this purpose a modified form of end cap 54 may be substituted in place of that shown in Figure 1, the modified construction being illustrated in Figure 3. The end cap 54' there shown is identical with the end cap 54 of Figure 1 except that an additional passage 14 communicateswith the passage 12' and is provided with a valve seat 18. A ball valve I8 cooperates with the seat I8 and is lightly urged to closed position by a light spring 18. The chamber 88 in which the ball and spring are mounted communicates with the conduit 82' and the connection 58 by a branch conduit 82. Thus the ball 18 acts as a check valve preventing flowfrom connection 58 to conduit 12 except through the ball valve 88'.

I When the modified end cap 54' is utilized, a-

modified piston construction is also utilized in place of the piston, i 8, this modification consisting merely in the omission of the flat 28, thus sealing the chamber l4 from the drain connection 32. The latter may be provided with an orifice of practically any size whatever since it Y is no longer critical in the operation of the'switch and serves merely to drain seepage which oc curs along the cylindrical surface of piston I8 and thus prevent pressure from building up on the packing l8. The coupling 58' may be provided with as small an orifice as may be desired.

The operation of this form of the invention is similar to that previously described except that when the pressure in the conduit 82' has risen sufilciently to open valve 88', the entire quantity of oil delivered therethrough is utilized to displace the piston I8 and shift the switchoperating plunger 42. As soon as the piston I8 has moved downwardly through its full stroke, the valve 88' again closes due to equalization of pressure on opposite sides thereof. Upward movement of the piston is prevented until the pressure in connection 58' falls to the point where check valve 18 may open, thus permitting oil to discharge from the chamber l4 through passages 74 and 82 to the connection 58'.

It will be noted that with either form of the invention small momentary pressure surges such as are bound to occur in many types of hydraulic systems will not depress the piston I 8 sumciently to shift the switch 38. In the first form of the invention described this result arises from the provision of the restricted drain to the chamber i4 which thus necessitates a supply of oil through the valve 88 in greater quantity than can escape from chamber l4 through the drain connection 32. In the second form of the invention momentary pressure surges are prevented from operating the switch by the provision of. the clearance at 52. This permits the piston I 8 to move downwardly a small amount without actuating the plunger 42. Also, due to the provision of a snap-acting switch some downward movement of the plunger 42 may be permitted before the switch is actuated. It will thus be seen that there is provided a pressure switch mechanism which is adapted to meet many varied requirements encountered in hydraulic transmission systems by the ready substitution of the simple and inexpensive bushings 32 and 58 and which may be said chamber at all times to conveniently adjusted as to its pressure response by adjustment of the spring plunger 1Q.

It will further be seen that the construction disclosed provides a switch which responds quickly to significant sustained pressure rises but which, on the other hand, is not aflected by momentary pressure surges, even though they may'rise to a value equal to or greater than the sustained pressure rise required to operate the switch.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A pressure responsive electric switch comprising a body member enclosing an expansible chamber having a movable element, a snap-acting electric switch connected for operation by said movable element, a passage communicatinfl with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage communicating with form a continuously open outlet duct andadapted to beconnected to a drain, a spring-loaded pressure responsive valve in said first. passage and adapted to maintain said passage closed at pressures below a predetermined degree, and a readily replaceable bushing in said second passage at the outside of said body.

2. A pressure responsive electric switch com-- prising a body member enclosing an expanslble chamber having a movable element, a snap-acting electric switch connected for operation by said movable element, a passage communicating with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage communicating with said chamber at all times to form a continuously open outlet duct and adapted to be connected to a drain, and a spring-loaded pressure responsive valve in said first passage and adapted to maintain said passage closed at pressures below a predetermined degree, said second passage having sufiicient fluid resistance to prevent actuation of the switch upon momentary pressure surges passing said valve.

3. A pressure responsive electric switch comprising a body member-enclosing an expansible chamber having a movable element, a snap-acting electric switch connected for operation by said movable element, a passage communicatin with said chamber to form an inlet conduit adapted to be connected with a variablepressure source, a second passage communicating with said chamber at all times to form a continuously open outlet duct and adapted to be connected-to a drain, a spring-loaded pressure responsive valve in said first passage and adapted to maintain said passage closed at pressures below a predetermined degree, and a pair of interchangeable bushings in said passages, accessible from the outside oi. the body andproviding predetermined resistance to fiow therethrough.

4. A pressure responsive electric switch comprising a body member enclosing an expansible chamber having a movable element, means providing a non-adjustable resilient bias for said movable element, a snap-acting electric switch connected for operation by said movable element, a passage communicating with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage communicating with said chamber at all times to form a continuously open outlet duct and adapted to be connected to a drain, and-an adjustable, spring-loaded, pressure responsive valve in said first passage and adapted to maintain said passage closed at pressures below a predetermineddegree, said outlet passage being provided with a mounting to receive any or a plurality of diflerent sized restrictor bushings.

' 5. A pressure responsive electric switch comprising a body member enclosing an expansible chamber having a movable element, means providing a non-adjustable resilient bias for said movable element, a snap-acting electric switch connected for operation by said movable element, a passage communicating with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage communicating with said chamber at all times to form a continuously open outlet duct and adapted to be connected to a drain, and an adjustable, spring-loaded, pressure responsive valve in said first passage and adapted to maintain said passage closed at pressures below a predetermined degree, said inlet passage being provided with a mounting to receive any of a plurality of diflerent sized restrictor bushings.

6. A pressure responsive electric switch comprising a body member enclosing an expansible chamber having a movable element, a cover member removably secured to said body and forming a closure for said expansible chamber, a map-acting electric switch connected ior operation by said movable element, a passage in said cover communicating with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage in one of said members communicating with said chamber at all times to form a continuously open outlet duct, a spring-loaded pressure responsive valve in said first passage and adapted to maintain said passage closed/at pressures below a predetermined degree, and a readily replaceable bushing in one of said passages at the outside of said body.

'I. A pressure responsive electric switchcomprising a body member enclosing an expansible chamber having a movable element, a snap-acting electric switch connected for operation by said movable element. a passage communicating with said chamber to form an inlet conduit adapted to be connected with a variable pressure source, a second passage communicating with said chamber at all times to form an outlet duct, a spring-loaded pressure responsive valve in said first passage and adapted to maintain said passage closed at pressures below a predetermined degree, and a check valve in said second passage 311d in parallel with said pressure responsive FERRIB '1'. HARRING'ION.

' CIJFFORD V. IOBIY. 

